Field of the Invention
The present disclosure relates to a separator for a nonporous lithium battery and a lithium battery including the same. More particularly, the present disclosure relates to a separator for a nonporous lithium battery, which can prevent permeation of moisture and oxygen, even though a large amount of electrolyte taken through an interchain space accelerates diffusion of lithium ions, as well as a lithium battery including the same.
Description of the Related Art A lithium-oxygen (Li—O2) battery has been given many attentions by virtue of its energy density 3-5 times higher than the energy density of a conventional lithium ion battery. This provides an advantage in that such a Li—O2 battery can extend the mileage of an electric vehicle upon each time of charging. It is very important to apply Li—O2 batteries successfully to electric vehicles.
Even though such a lithium-oxygen battery has high energy storage capacity, it is limited in cycle characteristics due to the partial irreversibility of a cathode, evaporation of electrolyte, unstable lithium metal interface caused by inevitable oxygen permeation into an anode, or the like.
Therefore, in order to solve the related problems caused by all of the battery elements, an approach to solve the problems in a systematic view is required. However, many related studies have focused on improvement of the reversibility of an air-cathode through the development of a high-efficiency catalyst and development of an electrode backbone and electrolyte.
Although such studies have improved cycle characteristics significantly, lithium metal stability during operation is still problematic and durability caused by inevitable contact with oxygen and moisture is also problematic. While electrolyte decomposition is carried out, water is produced from the reaction between a binder (poly(vinylidene fluoride)) and the intermediate (LiO2) of the main reaction, and the produced water causes production of lithium hydroxide (LiOH) on the lithium metal surface.
In addition, the other byproducts, such as Li2CO3 and ROCO2Li, may be formed on the lithium metal surface from the reaction between reduced electrolyte and oxygen. In fact, stabilizing the lithium metal surface is more difficult than solving the problem of reversibility of a cathode. This is because lithium metal is very sensitive to moisture and oxygen, and it is difficult to remove moisture and oxygen completely due to the open structure of a cathode.
To solve the above-mentioned problem, there have been some attempts to coat lithium metal with a ceramic/polymer protective film or to use a substitute anode material. However, such attempts cannot be fundamental solutions for the above-mentioned problem, because a protective film cannot survive continuously during cycles and use of a substitute anode material interrupts the advantages of a lithium-oxygen battery.
In addition, a lithium-sulfur battery has been given many attentions by virtue of its high capacity but has a difficulty in commercialization due to dissolution of polysulfides. Lithium polysulfides (Li2Sx, 4≤x≤8) with a long chain length generated upon the first discharge are dissolved into most water-insoluble electrolytes and diffused into a lithium anode. During this, the active material of a sulfur electrode is lost continuously and the interface of a lithium electrode becomes unstable due to the reaction in which lithium polysulfides participate. As a result, the battery undergoes degradation of coulombic efficiency (CE) during repeated cycles.
One of the methods for preventing such fatal lithium polysulfide dissolution is interrupting diffusion of lithium polysulfides while accelerating diffusion of lithium ions. Therefore, it is important to provide a separator that can accept lithium ions while interrupting diffusion of lithium polysulfides. There is a need for a separator capable of solving the problem of lithium dendrite growth that causes degradation of cycle characteristics.
Under these circumstances, there is an imminent need for developing a novel separator capable of solving the above-mentioned problems.